For clarification of common terms used in this document, an overview of certain cellular telecommunication system configurations is presented in the following.
Proposals for third-generation systems include UMTS (Universal Mobile Telecommunications System) and FPLMTS/IMT-2000 (Future Public Land Mobile Telecommunications System/International Mobile Telecommunications at 2000 MHz). In these plans cells are categorised according to their size and characteristics into pico-, nano-, micro- and macrocells, and an example of the service level is the bit rate. The bit rate is the highest in picocells and the lowest in macrocells. The cells may overlap partially or completely and there may be different terminals so that not all terminals necessarily are able to utilise all the service levels offered by the cells.
FIG. 1 shows a version of a future cellular radio system which is not entirely new compared with the known GSM system but which includes both known elements and completely new elements. In current cellular radio systems the bottleneck that prevents more advanced services from being offered to the terminals comprises the radio access network RAN which includes the base stations and base station controllers. The core network of a cellular radio system comprises mobile services switching centres (MSC), other network elements (in GSM, e.g. SGSN and GGSN, i.e. Serving GPRS Support Node and Gateway GPRS Support node, where GPRS stands for General Packet Radio Service) and the related transmission systems. According e.g. to the GSM+ specifications developed from GSM the core network can also provide new services.
In FIG. 1, the core network of a cellular radio system 930 comprises a core network CN 931 which has three parallel radio access networks linked to it. Of those, net-works 932 and 933 are UMTS radio access networks and network 934 is a GSM radio access network. The upper UMTS radio access network 932 is e.g. a commercial radio access network, owned by a telecommunications operator offering mobile services, which equally serves all subscribers of said telecommunications operator. The lower UMTS radio access network 933 is e.g. private and owned e.g. by a company in whose premises said radio access network operates. Typically the cells of the private radio access network 933 are nano- and/or picocells in which only terminals of the employees of said company can operate. All three radio access networks may have cells of different sizes offering different types of services. Additionally, cells of all three radio access networks 932, 933 and 934 may overlap either entirely or in part. The bit rate used at a given moment of time depends, among other things, on the radio path conditions, characteristics of the services used, regional overall capacity of the cellular system and the capacity needs of other users. The new types of radio access networks mentioned above are called generic radio access networks (GRAN). Such a network can co-operate with different types of fixed core networks CN and especially with the GPRS network of the GSM system. The generic radio access network (GRAN) can be defined as a set of base stations (BS) and radio network controllers (RNC) that are capable of communicating with each other using signaling messages. Below, the generic radio access network will be called in short a radio network GRAN.
The terminal 935 shown in FIG. 1 is preferably a so-called dual-mode terminal that can serve either as a second-generation GSM terminal or as a third-generation UMTS terminal according to what kind of services are available at each particular location and what the user's communication needs are. It may also be a multimode terminal that can function as terminal of several different communications systems according to need and the services available. Radio access networks and services available to the user are specified in a subscriber identity module 936 (SIM) connected to the terminal.
In UMTS specifications, a SIM is denoted with the term USIM (UMTS SIM). One mobile communication means (ME, mobile equipment) such as a cellular telephone can have more than one USIM connected to the terminal. This is useful, for example, for providing a person with a private telephone number with a first USIM and another number for work-related calls with a second USIM. The person can then receive calls to all of these telephone numbers with the same ME comprising the two USIMs, and bar any calls to any of these telephone numbers at his/her leisure. For example, the person can bar any calls to the work-related number at weekends and allow only calls to his/her private number. The USIMs may be separate IC cards, whereby the ME is required to have more than one USIM connector for connecting the USIMs, or a single IC card may comprise more than one logical USIMs.
In cellular telecommunication systems a single speech connection or data connection through the cellular telecommunication network is called a bearer. Generally, a bearer is associated with a set of parameters pertaining to data communication between a certain terminal equipment and a network element, such as a base station or an interworking unit (IWU) connecting the cellular network to another telecommunications network. The set of parameters associated with a bearer comprises typically for example data transmission speed, allowed delays, allowed bit error rate (BER), and the minimum and maximum values for these parameters. A bearer may further be a packet transmission bearer or a circuit switched bearer and support for example transparent or non-transparent connections. A bearer can be thought of as a data transmission path having the specified parameters connecting a certain mobile terminal and a certain network element for transmission of payload information. One bearer always connects only one mobile terminal to one network element. However, a bearer can pass through a number of network elements. One mobile communication means (ME, Mobile Equipment) may in some cellular telecommunication systems support one bearer only, in some other systems also more than one simultaneous bearers.
One old problem in cellular telecommunication systems is how to handle situations, in which the demand of services at some area in a cellular telecommunication system exceeds the capability of the cellular telecommunication system to provide such services. This problem is more severe in the UMTS system presently under development and other systems, where a mobile communication means (ME) can have more than one simultaneus connections i.e. bearers. A method is needed for determining, which current bearers are dropped or which new bearers are allowed in an overload situation.
One example of a typical overload situation is the handover of a connection to a crowded cell. One conventional way of handling this situation is simply to refuse the handover, which may result in a broken connection. The situation is more complicated, if the ME has several connections, and the new cell has spare capacity for only a subset of those connections. In such a situation, a method is needed for selecting which connections are serviced and which connections are refused.
One further example of a problematic situation is such a situation, when the capacity of a cell is already in full use, and one ME requests for example an increase in data transmission rate or a group of new bearers.